This invention relates generally to medical imaging devices, and more particularly, to alignment systems in medical imaging devices, such as an X-ray imaging device, computed tomography (CT) imaging device and/or magnetic resonance imaging (MRI) device.
A medical imaging device typically includes an imager and a generator. A patient or an object under examination is placed between the imager and the generator to image. Positioners and aimers emitting visible light, for example a laser, help in aligning the patient's body with respect to the central axis of the medical imaging device. The alignment of the patient or the object under examination with the medical imaging device is important in order to reduce, for example, the number of iterations required to obtain an acceptable image and to reduce radiation dosage to which a patient is subjected.
Known lasers used in medical imaging devices for alignment of an object include imager side lasers and X-ray generator side lasers. These lasers also may be integrated lasers or detachable lasers. Further, different laser output shapes, such as, for example, a cross type laser and dot type laser may be provided.
In order to minimize the amount of radiation scatter on people around the medical imaging device during an imaging process, the imager is typically placed above a patient and the generator is placed below the patient. The laser is placed on the imager side because otherwise the laser beams from the generator side would fall on the table and not on the patient.
On the imager side, the laser cannot be placed in the field of view (FOV) because it may result in artifacts in the image. Therefore, the lasers are placed outside the imager edges. Moreover, in known designs, two lasers are used to generate a cross, which is then used to aim the X-ray radiation at the object under examination. Both the lasers emit beams that intersect to form a cross a certain distance from the imager. Because the FOV on the imager side is larger than that on the generator side, the lasers also have to be positioned a sufficient distance apart. This increases the distance at which the cross pattern is formed. In order to minimize the distance at which intersection of the laser beams occur, the span of the lasers is increased. However, increase in the span of the lasers increases leakage of the radiation beyond the generator, which is harmful, for example, to the people standing around the generator.
In generator-side laser systems, a late intersection may be acceptable, as the patient is not placed close to the radiation source. However, in the case of imager side lasers, late intersection is a disadvantage, as doctors often tend to keep patients closer to the imager rather than the generator.
In dot type laser systems, the dot tends to get lost when positioning, for example, a body. Therefore, it is more difficult to align the object with a dot than a cross pattern. In addition, in dot type lasers, a partial reflector is used within the FOV. The X-rays at the inlet of the imager are much weaker and hence even a small object near the imager creates a significant artifact, as compared to the artifact created by the same object when it is closer to the X-ray generator. Thus, imager side lasers are generally detachable type so that after the laser is used, it can be removed and artifacts reduced. This is an additional operation for the operator that adds time and complexity to the imaging process. Even in detachable type lasers, the dot lasers are often preferred as they provide a reference to the central axis throughout the free space as compared to cross-type lasers, which form the cross at a distance.
Therefore, known alignment systems for medical imaging devices are typically difficult to use and add time to the overall imaging process.